Subscriber line circuit



Sept. 2, 1941. L. -H. ALLEN SUBSCRIBER LINE CIRCUIT Filed Sept. 18, 1940 to? at 11 :IUW

A T TORNEV is usually located conductors between the two stations.

will hereinafter be 'nal arrangement fied that the C station is engaged in using the Patented Sept. 2, 1941 seine SUBSCRIBER LINE CIRCUIT Lawrence H. Allen,

Summit, N. J., 'assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 18, 1949, Serial No. 357,248

4 Claims.

This invention relates to communication systems and particularly to subscribed line circuits in a telephone system.

The object of the invention is to provide improved facilities for special service to subscribers requiring an extension station at a point distant from his main station. Such distant extension station is spoken of as an ofi-premise station and at such a distance that it is impractical to provide more than a single pair of It, therefore, becomes necessary to perform numerous signaling functions between the two stations over this pair of wires as well as to provide for the transmission of voice currents thereover.

A feature of the invention is a relay arrangement located at the main station responsive to various conditions of the main and extension stations and the central oilice line. Particularly a feature of this invention is a relay arrangement which will prevent a breakofiice battery is disconnected the extension station, which referred to as the C (for conat the main station down when central from the line and trolled) station, is der the condition Where the station is employing the central office line certain relays have been operated'at the M (for main) station and are held so operated under control of the C station, special hold-over means are employed to prevent interference with this condition when the central ofiice battery is lost temporarily as sometimes happens under certain given circumstances.

Another feature of the invention is a busy sig- Whereby the M station is noticentral oflice line when the M station attempts to set up a connection between the M and C stations.

Still another feature is a circuit arrangement whereby the M station is supplied with talking battery from a local source when both the M station and the C station are effectively connected to the central ofiice line whereby the transmission is not adversely aifected by the metallic bridge across the central ofiice line supplied by the C station.

The drawing consists of a single sheet in the form of a circuit diagram showing a telephone line extending'from a central otfice to a main station and an off-premise controlled extension station.

The functions of this circuit are as follows:

1. To signal the M station on calls incoming from the central office;

2. To signal the C station on calls incoming from the central ofiice;

3. To place control of the central oifice line to the C station under control of the M station; 4. To signal the M station when the C station connected thereto. Since unis employing the central oifice line and the M station attempts to call the C station;

5. To signal the M station from the C station; 6. To signal the C station from the M station; 7. To provide for the M station holding a call on the central ofiice line;

8. To provide for releasing the held condition from either the M or C station;

9. To prevent the M station from signaling the C station when the C station is employing the central office line;

10. To supply talking battery to the M station when talking to the C station;

11. To supply talking battery to the M station when both M' and C stations are connected to 1 the central ofiice line;

V signaling is employed from the M to the C stathe tip conductor When a, call has central ofiice to tion. Relay 3is used for releasing the hold relay when the M station connects to the central ofiice line. Relay dis a holding relay used to hold the connection on the central ofiice line. Relay 5 is used as a supervisory relay to control the cutthrough equipment on calls from the C station to the central ofiice line. Relay 6 is used tohold up during dialing or switchhook flashing to maintain the cut-throughposition of calls from the C station to the central office line. Relay 1 is used to cut through the private line from the C station to the central office. Relay 8is used to hold over the cut-through condition in case of calls in the panel system when line relay battery is removed and before the sender is connected. Relay 9 is used to supply talking battery to the M station on calls between the M and C stations and on calls to the central ofiice when both M and C stations are connected. Relay I 0 is used to signal th M station on calls from the C station.

Calls between central ofiice and M Station-C station cut-017 0n incoming calls from the central office the ringer at the M station operates to signal such an incoming call. The central office is here represented by the rectangle H in which a ground connection is indicated as being connected to l2 and a battery connection is indicated as extending to the ring conductor l3. been properly extended in the the conductors l2 and I3 and ringing current applied thereto, such ringing curt -operate.

rent will flow through the condenser l4 and. the ringer l5 at the M station for.the purpose of signaling-the M station. Relay l also operates but performs no useful function providing the key It is placed in its open position. This key is of a type which may be placed and left in either the open or closed condition. The normal condition when the C station is to be cut off is open. Therefore, in this condition the operationof relay I" is without effect. in response to the incoming signal, operates the appropriate pick-up key IT and removes the handset I8 from its mounting l9, thereby closing the station circuit and causing the relay 3 to Thecircuit iforrelay 3 maybe traced from the ringconductor .13 through the normal contacts of armature 80f relay 1, thewinding of relay 3; the contacts 5 and 6 of key I1, contacts f Band I of key 20, contacts I and 2 of key 2|, the

the parallel circuitv .and resistance 3| of ring conductor 22 of the-station circuit, winding 23 ofthe induction coil', the-transmitter of the handset, the contacts 211 and228 :of the dial :29, through ''the inductance 3|] the filter'32, contacts I and 2 of the hook switch 33, tip conductor34-,' .springs 4 and 5'of key 20,:Springs 3and 4.of. key I]; the

tip conductor normal contacts of-armature l of-relay 1 to the l2. .-Relay 3 performs :1'10 useful function at this time. Oncallsoriginated at'the M station on central ofiice=1ine,-the central ofiice pick-up key I! isoperated 'and' callsomay be uoriginatedin the usual manner.

' Holding 7 The central office linemay be held by the operation 'ofthehold' key 2| in'thetelephone set atlthe M stationi The hold key-when operated opens the operating path for -the relay 3; causing relay 3"to be released. Key 2| also closes a circuit for operating relay 4' through its upper -wiridingin-series with=the centraloflice loop and station 'telephone s'et. winding of-relay 4 may 'The circuit for'the upper be 'traced from the point *whererelay 3 connected to-the rin'ging conducii a winding of relay 4, the 'lL springs l and 2 'of I and 3 of key" 2|. Thus of relay 4 is introduced in of the-'winding of :relay 3 in 4. operates-its lower winding will be connected acrossthe line'in a circuit 'which' may be traced ifromithe ringing conductor connected to the up- :per: winding: of relay rtact and armature of relay ing thereof, resistance 35,

:thenormal-contacts :Ofi armature l-of" relay 1. ".When the hold key 4, *throughthe front con- 4 and the lower windand thence through '2! is released; "the operated :-;;pick-up.key 'will be' released by the subscriber rat the "M station andi'the upper winding 'of relay station set will.

4'wil1 be :opened.' Relay 4, however, will be held operated through its .lower winding and thesubbeiidi'sconnected from the line. The holding condition is'released when the M .station with I thezhandset off its mounting 3 again operatesits pick-up .-key to operate the L relay .since .the L relay causes. the-'lower winding :of

1 relay. 4. tobershort-ecircuited Similarly, if .the C .station comes .on .the .line,. the operation of relay 5 operates .relay 6 which in .operationshort- .lcircuits the lower the holding-condition has winding. of .relay 4....through its armature 4 and front contact. Thus, after been established .it will be releasedunder control of either.the M or '0' station coming in on the central office line.

The subscriber atthe M station,-

.tral office line .tion and relay 1 operates.

Terminating calls on the central office line with the cut-017 key operated to connect the C stairon to the central office line In the case of a call terminating on the centhe ringer operates at the M sta- The operation of relay l operates relay 2 since the cut-off key 16 is now in the position shown. The operation of relay 2 connects the tip and ring of the central office line to the private line represented by conductors- 36 and 31 so that the ringing current now incoming from the central office line causes the ringer 38 at the C station to operate. If the C station answers the ringing signal with key 39 in its operated position where it eventually short-circuits the condenser 40, the relay 5 operates, causing the operation of relay 6, which in turn operates the cut-through relay 1. It will be noted that the windings of relay 5 are now included in series with the tip and ring conduc- C station and since relay 5 is designed to:operate on these currentsyit 6 uponoperating locks closes a circuit frombattery,

the winding of relay 3,the front contact andarmature of relay 5 through the contacts of key 16, the back contact and armature of relay ID to ground. Relay through its front contact and armature 2 so that this relay will be maintained operated even should the circuit through key lobe opened. Relay 6 also extends ground throughits armature 3 and front contactto the winding of relay L Relay 6 in operating removes ground from the lower contact of key 4|, thus preventing the M station from signaling theC station under the present circumstances.

The cut-through relay 1 when operateddisconnects the C station from the relay Ill and -:connects-it instead to the central oifice line.

This function is performed by armatures 3 and 6 "ofrelay 1. Under this condition the C station shaving. a metallic' bridge trips the ringing and I ofithe signalafter'the' C subscriber's set is connected to the windings "of M station. wThe operation I retardation coil 42 :Under this condition both the M and C stations the conversation may take place. 1 In case the M station responds to the ringing station,-the 'M station relay 9, which supplies talking battery to the of relay 9 bridges the across the central ofiice line.

may converse on the central office line, and since the M'station now has a local battery supply the :transmission is not adversely affected by the metallic bridge of the C station across the central ."If-the M station had responded to the ringing signal first, it would have tripped ringing as'it would have supplied a metallic bridge to the cen- 'tral 'ofiice. If the C station then answers, there- 2lays5; 6 and 1 operate-and when relay 1 operates it connects the C station across the line and furnishes battery supplied through relay 9 tothe M station. When both theM and C stations are "rconn'ected to the central office'line it is necessary,in dial systems aizfiashingrecall, to immediately provide a hold- .through relay 1 bridges the and in manual systems with When the C station disconnects relay 5releases,

Bto release and in turn .The release of the cut- M station across the causing the slow relay to release the relay 1.

. central-office line to. maintain the connection in place of the retardation coil 42.

In order to be able to make the central 'ofiice call from the C station, the cut-01f key [6 at the M station must be in the position shown. When the C station originates a call, the key 39 is'operated to its closed position and the handset is removed from the mounting, which thereby places a metallic bridge across the line operating the relay 5 on battery supplied through relay I3. Under this condition relay I is not operated because its windings are differentially connected. The operation of relay causes the operation of relays ,6 and 1 to operate as described hereinbefore, causing the private line to cut the C station through to the central oifice. The C station may then dial, in case of dial systems, or originate a call manually as in manual systems. Relay 5 may follow dial pulses but the combina tion of the slow relay 6 and relay 1 insures against the cut-through relay 1 releasing during dialing.

Holding C station out through on loss of central ofiice battery In the case of the panel system when line relay battery may be removed before the sender is connected, relay 5 will release, causing the release of the relay 6. Under these circumstances the cut-through relay 1 remains locked up under control of the back contact of the hold-over relay 8. This circuit may be traced from battery, the winding of relay 1, armature 5 and front contact of relay 1, armature and back contact of relay 8, armature 8 and back contact of relay 9, the closed circuit through key l6 and the back contact and armature of relay ID to ground. When battery is restored to the tip and ring of th line, relay 5 and the hold-over relay 8 receive operate current together. The relay 5 usually operates first, operating the relay 6, thereby holding the cut-through relay 1. Otherwise the operation of the hold-over relay 8 unlocks the cut-through relay 1 but before it has had time to release, ground is supplied to its winding through the front contacts of both the relay 5 and the hold-over relay 8. The relay 6 follows the operation of relay 5 and this in turn applies ground to the cut-through relay 1. The hold-over relay 8 releases upon the operation of the relay 5. Thus the cut-through relay 1 is held operated and the line is maintained in the cut-through condition when the lines l2 and 43 within the central office II are opened.

Calls from the M to the C station When the pick-up key 28 is operated at the M station relay 9 is connected to the subscribers set providing talking battery. With the handset removed from its mounting the operation of relay 9 opens the tip on the ring of the central ofi'ice line so that incoming calls will not cause ringing to be applied to the private line. Ringing current is connected to the front contacts of relay 2 through the armatures 9 and this ringing current may be extended to the C station by the momentary operation of key 4|, which causes the operation of relay 2.

When the C station responds to the ringing which may be made on a signal basis through the proper manipulation of the key 4| to enable the C station to identify the nature of the incoming call, the normal position of the key 39 places a condenser 40 of the subscribers set in series with the line, preventing the operation of 1 and 3 of relay 1 the relay 5; The C station, in all cases, obtains its talking battery from the local supply.

Calls originated from the C station to the M station I 'When the C station operates key 42, its ground is'connectecl to the ring of the private line, causing the operation of relay l0. Relay III has been described hereinbefore as being difierentially connected andhence with ground now applied to its lower winding and with its upper winding opened by condenser 40, this relay will become operated- Relay I 0 in operating causes the buzzer 43; to operate at the M station. :The M station in responding to the buzzer signal operatesthe pick-up key 20 for the private line connecting the telephone set to the windings of relay 9.

Anti-side tone network at C station When the C station employs a resistance network connection in the anti-side tone circuit, it is so connected that there is no anti-side tone feature for calls from the C station to the M station. In case of calls from the C station to the central ofiice, however, the resistance network is in circuit.

Busy signal at M station when G station is on a central ofiice line In case the M station attempts to originate a call to the C station at a time when the C station is engaged in a call on the central oflice line, a steady buzzer signal is given the M station when the handset is removed from the mounting. Under the cut-through condition of the private line the cut-through relay 1 is operated as described hereinbefore. When the M station bridges the tip and ring leads for connecting the M to the C station, ground is applied from the make contacts of the cut-through relay 1 through the M station to the battery connected through the winding of the relay I 0. This circuit may be traced from ground, the front con-tact and armature 2 of relay 1, contacts 3 and 4 of key 20, tip conductor 34 through the circuit of the M station, ring conductor 22, springs l and 2 of key 2|, springs 1 and 8 of key 20, armature 1 and its front contact of relay 1, the lower winding of relay I 0 to battery. This operates relay I 0 which in turn operates the buzzer 43. The buzzer continues to operate as long as the handset is off its mounting and the private line pickup key is operated.

What is claimed is:

1. In a telephone system, a central ofiice line extending to a subscribers station equipped with an extension station, a two-conductor connection between said subscribers station and said extension station, transmitter and signaling battery being supplied over said central oihce line, and means at the .said subscribers station for automatically maintaining an established'connection from said central ofiice line to said extension station when said transmitter and signaling battery at said central ofiice is disconnected from said central office line.

2. In a telephone system, a central office line extending to a subscribers station, an auxiliarysubscribers station, an activating switch at said subscribers station for conditioning apparatus thereat to give central ofiic line service to said auxiliary line, said apparatus including a cutthrough relay for transferring control of said central office line from said subscribers station to said auxiliary :statio'npand ahold-over relay tral ofiice end of said central office line are infor preventing. the deenerglzation of said cutterrupted.

through relaywhen the normal connection of 4. In a telephone system, a central oifice line central oifice battery to said central oflice line extending to a subscribers station equipped with is temporarily broken. 5 an extension station, a two-conductor connection 3. In a telephone system, a central office line between said subscribers station and said exextending to a subscribersstatioman auxiliary tension station, transmitter and signaling batstation associated with said first station by a tery being supplied over said central office line, line extending from said first station to said local transmitter battery and a metallic holding auxiliary station, relay means at said first sta- 10 bridge and means to substitute said local transtion for variously interconnecting saidtwo stamitter battery and said metallic holding bridge tions, said central office line and said line ex for said central oflice transmitter battery respontending from said first station tosaid auxiliary sive to the simultaneous use of said central office station, a master switch at said first stationfor line by both said stations, and means at the said giving and depriving said auxiliary switch con- 15 subscribers station for automatically maintaintrol over said relay means and included in said ing an established connection from said central relay means, a hold-over relay for maintaining office line to said extension station when said an established connection between said auxiliary signaling battery at said central office is disconstation and said central office line over a period nected from said central oflice line.

during which the normal connections at the cen- 20 LAWRENCE H. ALLEN. 

